Many of the numerous communications services which utilize the radio frequency portion of electromagnetic spectrum each operate over one or more broad ranges of frequencies, including aeronautical mobile (3-23 MHz), amateur radio (2-30 MHz), government (25-50 MHz and 30-90 MHz), land mobile (2-50 MHz), and marine mobile (3-22 MHz), to name a few. Heretofore antennas for such services operating in bands from very-low frequencies ("VLFs") through the low end of ultra-high frequencies ("UHFs") either had to be changed for every different narrow range of frequencies, or manually or electronically rematched and/or retuned so that the antenna would have acceptable operating characteristics such as low VSWR and high gain over the entire frequency range of interest. These characteristics were particularly difficult to achieve in mobile applications where antennas had to be strong, light-weight, easy to use and of low-profile.
One such well known, broad band vertically polarized monopole mobile antenna, designed for use with frequencies from about 30 MHz to 76 MHz, is disclosed in the article by Helmut Brueckmann entitled "A New Approach to Broadband Vehicle Antennas", 1958 IRE National Convention Record. Part 8, pages 19-27. The impedance of this antenna varies so widely over these frequencies that four separate matching and tuning circuits, manually switched in and out by the user, must be employed to tune the antenna.
Recently electromagnetic communication systems have begun to employ broad bandwidth techniques, such as the so-called frequency-agile or frequency-hopping systems in which both the transmitter and receiver rapidly and frequently change communication frequencies within a broad frequency spectrum in a manner known to both units. When operating with such systems, antennas having multiple matching and/or tuning circuits that must be switched, whether manually or electronically, with the instantaneous frequency used for communications, are simply inadequate. Instead, it is imperative to have a single antenna reasonably matched and tuned at all frequencies throughout the broad frequency spectrum of interest.